In a high-voltage propelled vehicle (HVPV), such as a hybrid-electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), a fuel cell electric vehicle (FCEV), or a purely electric vehicle (EV), an energy storage system (ESS), for example a battery pack, can provide a source of at least a portion of the power necessary for propelling the vehicle. The engine or fuel cell can shut off or power down when the vehicle is idling or at a standstill in order to further conserve fuel, depending on the particular design of the vehicle. The ESS itself contains or stores relatively high voltage, which is transmitted to one or more vehicle devices, such as one or more motor/generators, via a specially configured high-voltage bus having a positive and a negative conductor or “rail”. The ESS in turn is isolated from the various vehicle conductive structures and surfaces, and from the vehicle chassis itself, in part by selectively opening one or more electrical relays or contactors under certain operating conditions, such as during vehicle shutdown and/or under certain fault conditions, by opening one or more contactors.
Electrical contactors or relays serve to confine high voltage within the ESS during the vehicle shutdown process, as well as during certain fault conditions. Contactors helps to ensure that power to the load is shut off or interrupted when the contactors are de-energized. Contactors also help ensure that the high-voltage energy is transmitted to a load, such as a motor/generator, only when the contactor is properly energized or closed. However, under certain fault conditions the leads of one or more of the contactors may weld together, thus potentially rendering the contactor ineffective for its intended purpose. Therefore, the detection or diagnosis of such a welded contactor condition can be desirable, in particular for certain preventive or corrective maintenance purposes.
A normally-open contactor can help to ensure that electrical power to the load is shut off or interrupted when the contactor is de-energized, and that the high-voltage is transmitted to a load, such as the motor/generator, only when the contactor is properly energized or closed. However, under certain fault conditions the leads or contacts of one or more of the contactors can physically weld together, which in turn might affect the controllability of the flow of power from the ESS. While the presence of both welded contactors in a two-rail relay can be detected using diagnostics provided by a vehicle's control system, such diagnostics measure a drop in voltage when the contactors are opened, and require that other control modules to be active and communicating with the ESS for a predetermined period of time after the contactors are opened. Additionally, such voltage drop methods cannot detect the presence of a single welded contactor in a two-rail relay, particularly on the negative rail of a high-voltage bus. Other fault conditions, such as disconnected high-voltage vehicle components, are generally detected using communications intensive messaging processes that may be less than optimal for certain purposes.